Coelom
Advantages of the fluid-filled coelom:
faster distribution of materials throughout body
digestive tract can become longer, suspended in coelom; longer digestive tract is more efficient in nutrient absorption
provides room to arrange different organs in different positions; more room enables gonades to become bigger; bigger gonades can produce more sperm/egg
body becomes more flexible ? better motility
contact between endoderm and mesoderm remains ? better coordination of organ development and placement during embryology (separation of endoderm and mesoderm in pseudocoelomates limits tissue specialization)